It's the difference between the three-month T-bill rate and three-month Libor - a measure of the perceived riskiness of interbank lending. Last month everyone thought it was falling. Well, it's back up again. And worse news from the WSJ - banks may have been lying about Libor...

The growing suspicions about Libor's veracity suggest that banks' troubles could be worse than they're willing to admit.

The concern: Some banks don't want to report the high rates they're paying for short-term loans because they don't want to tip off the market that they're desperate for cash. The Libor system depends on banks to tell the truth about their borrowing rates. Fibbing by banks could mean that millions of borrowers around the world are paying artificially low rates on their loans. That's good for borrowers, but could be very bad for the banks and other financial institutions that lend to them.

No specific evidence has emerged that banks have provided false information about borrowing rates, and it's possible that declines in lending volumes are making some Libor averages less reliable. But bankers and other market participants have quietly expressed concerns to the British Bankers' Association, which oversees Libor, about whether banks are reporting rates that reflect their true borrowing costs, according to a person familiar with the matter and to government documents. The BBA is now investigating to identify potential problems, the person says...

The article continues to say that the real Libor rate could be up to 30bp higher than reported.

Well, that's great.